I have a 1 MVA diesel generator, 11 kV line to line (medium voltage.) To test this generating set, I connected it to industrial load (heaters only with a pf = 1 via a 11 kV to / 380 V transformer.

I now measure that the overall power factor is 0.44 lag and this value is far too low.

Does anyone have any idea of what the problem is?

Here is the transformer data:

transformer data

Here is the measured result:

the measured result.


The power factor of the generator is defined by the load. If the load power factor is unity, the current in the load will be in phase with the voltage.

You either have a measurement error, a fault or your load is not resistive.

Can you post a diagram of the meter setup?

  • \$\begingroup\$ The load is not resistive if the heater voltage controlled by an electronic controller. An electronic voltage controller will cause harmonic current distortion and reduce the total power factor. If the load is very light, the transformer magnetizing current could have an effect. If the transformer has an active cooling system, that could also be a factor. \$\endgroup\$ – Charles Cowie Feb 26 '17 at 20:29
  • \$\begingroup\$ the heater's voltage is not controlled by any controllers ,but the generator is producing 11kv through an Automatic voltage controller (AVR) embedded in the alternator itself , and the 11KV is directly connected to the primary coil of the transformer ,and the secondary is connected directly to the load bank which consists of 400v heaters . \$\endgroup\$ – Ahmed Khedr Feb 26 '17 at 21:29
  • \$\begingroup\$ and one more important thing , that transformer hadn't been used for 3 years, there was no maintenance during that period . I only added some oil to reach the max mark . \$\endgroup\$ – Ahmed Khedr Feb 26 '17 at 21:31
  • \$\begingroup\$ there is also a cooling system "ONAN" Oil Natural Air Natural \$\endgroup\$ – Ahmed Khedr Feb 26 '17 at 21:37
  • \$\begingroup\$ @Ahmed can you post a diagram of your meter setup? \$\endgroup\$ – skvery Feb 27 '17 at 4:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.